A variety of wireless communication services utilizing wireless communication networks and wireless communication terminals have been developed in tandem with the rapid progress in electronic and communication technologies. Conventional services include wireless voice communication services providing mobile communication terminal users with wireless voice communication regardless of time and space, and text message services supplementing the voice communication services.
In line with the development of the wireless Internet, wireless Internet services have also launched in recent years, which provide mobile communication service subscribers with Internet communication services via wireless communication networks, so that many enterprises are conducting R&D on the wireless Internet.
Among various wireless Internet services using mobile communication terminals, much attention has recently been paid to an LBS (Location Based Service) due to its wide range of usefulness and convenience. The LBS refers to a communication service for positioning a mobile communication terminal and providing additional information based on the positioning result. The LBS is used in various fields and situations, including emergency aid requests, responses to crime reports, GIS (Geographical Information System) for providing information regarding adjacent areas, differentiation of mobile communication fees according to locations, traffic information, vehicle navigation, logistics control, location-based CRM (Customer Relationship Management), etc.
A location measurement scheme for providing a mobile communication terminal with the LBS is largely divided into a network-based scheme in which the location of a mobile communication terminal is measured by determining the location on a software basis by using a propagation environment (i.e. cell radius of a base station in a mobile communication network), a handset-based scheme using a GPS (Global Positioning System) receiver provided in a mobile communication terminal, and a hybrid scheme combining both the schemes.
The A-GPS scheme is a type of handset-based scheme, which can be used in both a network based on European GSM (Global System for Mobile Communication) using the TDMA (Time Division Multiple Access) wireless access scheme and a network based on IS-95 using the CDMA (Code Division Multiple Access) wireless access scheme. According to the GSM wireless access scheme, a mobile communication terminal is positioned by transmitting/receiving messages through an OMA SUPL (Secure User Plane Location) interface between the mobile communication terminal incorporating a GPS receiver and the SPC (SUPL Positioning Center) within the GSM network and through an SUPL POS for A-GPS location measurement within the OMA SUPL (i.e. GSM A-PGS protocol incorporating an RRLP (Radio Resource Location Protocol)). This type of positioning is very accurate because satellite signals are received from at least four GPS satellites to measure the location of a mobile communication terminal. Such an A-GPS system includes an SPC (SUPL Positioning Center) for receiving satellite signals received by a mobile communication terminal and calculating the location thereof, and an SLC (SUPL Location Center) for processing the calculation based on information regarding base stations within the GSM mobile communication network or associating the information with other systems.
The E-OTD (Enhanced Observed Time Difference) scheme is a typical network-based location measurement scheme, and has been standardized through LCS Release 98 and 99 by the GSM standardization committee of the European TDMA-based GSM scheme using the TDMA wireless access standard. According to the E-OTD scheme, a mobile communication terminal is positioned by calculating the relative differences in time of arrival and distance between signals received from at least three base stations. In other words, the E-OTD scheme uses a combination of various time difference concepts, including OTD (Observed Time Difference), RTD (Relative Time Difference), GTD (Geometric Time Difference), and the like, for network-based location calculation.
The OTD refers to the difference in time of arrival of signals from two base stations to a mobile communication terminal, and can be obtained by measuring the UE Rx-Tx time difference type 2 parameter in a GSM-based mobile communication terminal.
The RTD refers to a parameter used to obtain the difference in starting time of signals transmitted from two base stations, and can only be measured by equipping each of the base stations with a separate measuring device, that is, an LMU (Location Measurement Unit). This means that, in performing network location calculation in the E-TOD scheme, the RTD as well as the OTD must be obtained in order to evaluate the key parameter necessary for network-based location calculation recommended by the GSM standard, that is, “GTD=OTD−RTD”.
According to network-based location measurement technology, data (PPM, OTD, RTD, etc.) measured by a mobile communication terminal and an LMU is transmitted to a location measurement server according to a protocol (IS-801, RRLP, RRC, etc.) prearranged between the mobile communication terminal and the server, and the location measurement server performs a function of measuring the location of the corresponding mobile communication terminal by using the data (PPM, OTD, RTD, etc.) measured by the mobile communication terminal. The location measurement server conducts network-based location measurement (i.e. location measurement scheme in which a server side measures the location of a terminal that has requested location measurement, excluding location measurement schemes using GPS satellites), and transmits a result thereof to the requesting party (SLC, CP (Contents Provider), mobile communication terminal that has requested the corresponding service, etc).
The network-based location measurement technology includes a cell ID scheme using cells within a base station radius, an AOA (Angle of Arrival) scheme in which a base station conducts location calculation by receiving signals transmitted by a mobile communication terminal and calculating LOB (Line of Bearing), a TOM (Time of Arrival) scheme in which a mobile communication terminal calculates location based on the time of arrival of radio waves transmitted from at least three base stations, and a TDOA (Time Difference of Arrival) scheme in which a mobile communication terminal measures the difference in time of arrival of pilot signals received from three base stations to calculate the difference in distance between the base stations and determines the point of intersection of two resulting hyperbolas as its location.
However, the aforementioned conventional network-based location measurement schemes have the following problems:
Firstly, when data regarding parameters (i.e. time and distance) measured by a mobile communication terminal or a mobile communication network is used for triangulation or calculation of the point of intersection of hyperbolas, repeaters heavily affect a result thereof. This means that, in the case of using repeaters, data regarding the time and distance between a base station and a mobile communication terminal, measured by the mobile communication terminal, is delayed relative to the original data, which degrades the accuracy of location measurement.
Secondly, in the case of triangulation using time and distance measurement parameters in an asynchronous mobile communication network (GSM, W-CDMA, etc.), the result of location measurement can be obtained from the calculation formula only by measuring not only the OTD measured by a mobile communication terminal, but also the RTD value measured by an additional LMU equipped with separate GPS equipment. Considering that it has little merit per investment to additionally install LMUs in the entire mobile communication network for the network-based location measurement, network-based location measurement using triangulation cannot be used in a region where no LMU is installed.
Thirdly, when a base station is rearranged, the latitude and longitude data of the rearranged base station is not instantly reflected, so that it is impossible to confirm whether or not the latitude and longitude data referred to for location measurement is identical to the latitude and longitude data of the rearranged base station.
Finally, since characteristics regarding mobile communication base stations and sectors are different according to network-based location measurement technologies, excessive human and material resources are required to optimize parameters that are differently used by the respective base stations or sectors for the purpose of improving the accuracy of location measurement, which slows down the commercialization.